No. 2.] EYES OF POLVCHJETOUS ANNELIDS. igy 



SPIONIDiE, 



A species of Polydora having long setal hooks upon the 

 posterior somites as in P. hamata of Webster, but inhabiting 

 soft tubes upon the piles of wharves, has four minute eyes buried 

 in the superficial ganglionic layer of the brain. Each eye is a 

 cup of dark brown pigment granules, partly surrounding a clear 

 lens that does not appear to be separated from the surrounding 

 brain mass. 



A similar minute eye is seen in sections of Polydora commen- 

 salis Andrezvs. 



In a peculiar and apparently undescribed Spio, taken at 

 Wood's Holl, there are four eyes, the anterior larger and farther 

 apart, as is the rule in the higher Polychsetous annelids. Each 

 is buried amongst the ganglion cells of the brain, and has the 

 same simple structure as in Polydora (Fig. 71). In some sec- 

 tions there is little doubt that the pigment lies in a few, a very 

 few, cells between the nucleus of the cell and the part next 

 the lens. 



The Spionidae thus present a state of simplification that may 

 be regarded as in some sense a reduction from the degenerated 

 condition found in Arabella (Fig. 47) ; yet, at the same time, 

 it appears to be largely a retention of larval characteristics. 



Jacobi (10) has figured the eyes of P. quadrilobata and P. 

 ciliata as bean-shaped masses of pigment granules applied to a 

 hemispherical lens, and sending a few nerve fibres to the brain. 

 The whole is imbedded in the epidermis, while continuous with 

 the brain. The anterior eyes have scattered pigment near 

 them, and are irregular, thus giving the appearance of more 

 than four eyes. This would favor the supposition that the eyes 

 of the Spionidae are to some extent degenerate structures. 



ToMOPTERIDjE. 



Examination of an immature specimen of Tomopteris, taken 

 off the New England coast by the U. S. Fish Commission, 

 shows that the two eyes are buried in the brain (Fig. 72). In 

 each we recognize a lens, somewhat granular, as in Eulalia, 

 separated from the pigment cup by a clear zone that may be 

 interpreted as the rod-like ends of a few very large cells. The 



